The combustion of fuel and oxidant to provide heat is used in a large number of commercial furnaces in such industrial applications as the generation of electricity, the production of steel and other metals, the production of glass, and the treatment of wastes. Typically the oxidant employed in the combustion process is air which contains a substantial amount of nitrogen. In the course of the combustion reaction, nitrogenous species in the fuel and nitrogen in the air are oxidized to form NOx. Other combustion gases, which typically include carbon dioxide and water vapor are also formed.
The emission of NOx from industrial and other furnaces has been shown to have a serious impact on both environmental quality and human health. The compounds cause acid rain, are a factor in the formation of ground level ozone, and have been implicated in the formation of fine particulate.
One approach to reducing NOx emissions from a combustion reaction is reburning wherein fuel is provided to the NOx-containing combustion gases to react with the NOx and form nitrogen gas. Typically the fuel employed for the reburning is methane or natural gas.
It is desirable to use a less expensive fuel such as coal or other granular carbonaceous fuel for reburning to reduce NOx emissions. However, the use of such fuels can reduce the efficiency of the reburning because longer contact times are necessary, and can result in the ash having a high carbon content causing the need for further processing steps for the ash.
Accordingly, it is an object of this invention to provide an improved method for reducing NOx emissions from a combustion reaction using reburning with a granular carbonaceous fuel.